The present invention relates to a reducing agent supply apparatus for supplying reducing agent to an exhaust gas passageway of an internal-combustion engine and an internal-combustion engine exhaust gas purification apparatus including such a reducing agent supply apparatus.
Conventionally, in an exhaust gas passageway of an internal-combustion engine included in a vehicle or the like, an exhaust gas purification apparatus for purifying nitrogen oxides (NOx) contained within exhaust gas is provided. One aspect of such an exhaust gas purification apparatus is an exhaust gas purification apparatus that includes: an NO purification catalyst for speeding up reduction reaction of NOx; and a reducing agent supply apparatus for supplying liquid reducing agent to within an exhaust gas passageway upstream of the NOx purification catalyst.
FIG. 13 illustrates an example of a reducing agent supply apparatus 220. The reducing agent supply apparatus 220 includes: a pump 223 for sucking up and pumping liquid reducing agent, such as unburnt fuel or ammonia aqueous solution, stored in a tank 221; a reducing agent injection valve 225 for injecting the pumped liquid reducing agent to within an exhaust gas passageway; a reducing agent supply passage 227 for guiding the liquid reducing agent pumped by the pump 223 to the reducing agent injection valve 225; a reducing agent return passage 229 connected between the reducing agent supply passage 227 and the tank 221; a pressure sensor 231 for detecting a reducing agent pressure Pu within the reducing agent supply passage 227; and a control unit 240 for controlling the pump 223 and the reducing agent injection valve 225.
Such an reducing agent supply apparatus 220 needs to perform injection control of liquid reducing agent considering the amount of NOx contained within exhaust gas, the reducing efficiency of NOx and the like so that an appropriate amount of liquid reducing agent will be supplied to within the exhaust gas passageway in just proportion. In order to do this, the injection amount of liquid reducing agent is controlled by adjusting when the reducing agent injection valve 225 is opened, while the pressure Pu of the reducing agent supplied to the reducing agent injection valve 225 is controlled so as to be maintained at a predetermined target pressure Pu_tgt.
Here, one way of controlling the reducing agent pressure Pu so as to be maintained at the target pressure Pu-tgt is to feedback-control the output of the pump 223 based on the difference ΔPu between the reducing agent pressure Pu detected by the pressure sensor 231 and the target pressure Pu_tgt (see JP-A-2011-117441).